407 dodgy brakes

[wacuda]

hi guys my 05 407 diesel has a wierd brake issue..every now and then the pedal will go to the floor..works fine on the second pump..fluid is full..booster holds vacuum...vacuum lines look good...newish pads..calipers seem firm...99 times the pedal only moves 1" and the brakes work good but that 1 time it travels to the floor..its almost like a bent disc pushing the piston too far back and it takes 2 pumps to get it back out but the discs are straight....any clues..thanks

 

[dacia4x4]

two areas I would look at would be wheel bearing play which would as you describe knock brake pads back causing low pedal on first application.failing that I would look at brake master cylinder having either a faulty primary cup on one of the two circuits or foreign material sitting in lower portion of master cylinder bore and being picked up under primary cup occasionally…..jim

 

[wacuda]

thanks jim..wheel bearings are good....i will try a fluid flush..cheers